1. Field of the Invention
The present invention relates to a deflecting mirror configured to deflect and scan a light beam such as laser beams. In addition, the present invention relates to an optical scanning device, an image forming apparatus, and image projecting apparatus, which are equipped with the deflecting mirror.
2. Discussion of the Background
Deflecting mirrors are broadly used for various devices such as optical scanning devices, image forming apparatus, image projecting apparatus, barcode scanners, and laser radars. An electrostatic force, electromagnetic force or piezoelectric force is used for driving such deflection mirrors.
Deflecting mirrors using an electrostatic force use a parallel-plate electrode or a comb-shaped electrode. With recent improvements in fine processing technology, comb-shaped electrodes can generate a relatively large force. However, a desirable light deflection angle cannot be obtained even by a deflecting mirror using such an improved comb-shaped electrode. Therefore, it is necessary to apply a high voltage for driving the deflecting mirror. Increasing the driving voltage for a deflecting mirror causes problems such that the parts of the electric source used for the deflecting mirror become large in size; and costs of the deflecting mirror increase.
Deflecting mirrors using an electromagnetic force have to use a permanent magnet, which is to be arranged outside the mirrors. Therefore, the deflecting mirrors have complex configuration (i.e., poor productivity), thereby making it impossible to miniaturize the deflecting mirrors. Recently, investigation on deflecting mirrors using a magnetostrictive film has been made. However, since such a magnetostrictive film has poor magnetic properties, the resultant deflecting mirror has poor deflection properties. In addition, a problem in that when a current is flown in the coil, an excessive amount of heat is generated, resulting in increase of electric consumption is caused.
Deflecting mirrors using a piezoelectric force can generate a large force even by a small electric power although the deflecting mirrors need a relatively large driving voltage. Although deflecting mirrors using a piezoelectric force can generate a large force, the degree of distortion of the mirrors is small. In attempting to enhance the distortion, piezoelectric devices having a unimorph or bimorph structure such that a piezoelectric material and an elastic beam-like member are overlaid to change a small degree of in-plane distortion caused by piezoelectricity to a relatively large degree of warping have been investigated.
Published unexamined Japanese patent applications Nos. (hereinafter referred to as JP-As) 07-199099 (corresponding to U.S. Pat. No. 5,579,148) and 2008-83603 (corresponding to published US application No. 20090185254) have disclosed deflecting mirrors having a piezoelectric unimorph structure.
JP-A 2008-83603 discloses a technique in that a piezoelectric body having a specific length is arranged only on one side (fixing portion side) of a beam portion of a frame portion, and two beam portions (hereinafter referred to as driving beam portions) located on both sides of a connection point of the mirror supporting portion with the frame portion are driven in the opposed directions (i.e., reversed-phase driving), thereby imparting a moment thereto. Namely, since the two driving beam portions are driven in the opposite directions, both the movements of the driving beam portions are limited, resulting in deterioration of driving efficiency.
Thus, the optical scanning element disclosed in JP-A 2008-83603, in which a piezoelectric body is arranged on a portion of one side (fixing portion side) of a driving beam portion, has poor driving efficiency.
Because of these reasons, a need exists for an optical scanning element (deflecting mirror) in which a mirror can be deformed at a large angular amplitude even by a relatively low driving voltage.